The present disclosure relates to reducing the risk of internal condensation forming within a liquid cooled computer system during manufacturing test.
Computer systems typically include cooling mechanisms to cool components that generate heat, such as processors, co-processors, etc. These cooling mechanisms include heat sinks coupled to a component to dissipate the heat, conventional fans to blow air over the component, or a combination of a heat sink and a conventional fan to dissipate heat. High-end computer systems, however, have components that generate a substantial amount of heat, which conventional cooling methods are not able to dissipate. As such, high-end computer systems utilize a liquid cooled system that includes “plumbing” coupled to critical components to dissipate the heat, similar to an automobile radiator cooling system.
Liquid cooled systems often carry cold water set at a “system setpoint” temperature to cool the internal components. During normal operation, the system setpoint temperature is set within a temperature range at a level that adequately cools the internal components, which is typically lower than that of the surrounding air. Trade-offs of determining the system setpoint temperature involve determining whether the energy expended to cool the liquid produces a corresponding benefit in having a lower operating temperature of the logic of the computer system.
Another consideration when setting the system setpoint temperature is to maintain the system setpoint temperature at or above the dew point of the surrounding air in order to avoid condensation build-up inside the computer system. As those skilled in the art can appreciate, the dew point is a temperature at which water vapor in air at constant barometric pressure condenses into liquid water at the same rate at which it evaporates. The dew point is associated with relative humidity such that a high relative humidity indicates that the dew point is closer to the current air temperature. For example, a relative humidity of 100% indicates that the dew point is equal to the current air temperature and that the air is maximally saturated with water. As such, condensation forms on the computer system's liquid cooled plumbing if the system setpoint temperature is set below the dew point of the surrounding air.
When high-end computer systems undergo environmental testing at a test facility, the test facility performs temperature bias thermal stress tests to test the cooling system. The temperature bias thermal stress test involves a “hot” bias test where the system setpoint is set above a maximum system setpoint temperature, and a “cold” bias test where the system setpoint is set at or below a minimum system setpoint temperature. For example, assuming the specified system setpoint temperature range is 12 degree Celsius to 22 degree Celsius, the cold bias test may execute at 10 degree Celsius and the hot bias test may execute at 24 degree Celsius to ensure an operating margin of the liquid cooled system.
The “cold” bias test is problematic, however, if the desired cold bias system setpoint temperature is set below the dew point of the surrounding test facility environment. As discussed above, condensation forms on the plumbing if the system setpoint temperature is below the surrounding environment's dew point. Once condensation has formed on the plumbing inside the computer system during manufacturing test, the condensation often leads to system failure because of wet circuitry or by the deposition of residues left behind after the condensation has evaporated.